The present invention relates to a liquid crystal display device, and particularly, to a liquid crystal display device with a register-type gamma reference voltage generating unit inside a data driving IC, to remove a source block dim phenomenon in a Chip on Glass (COG) cascade structure, and a driving method thereof.
In general, a Liquid crystal display (LCD) device has an optical anisotropy that it obtains when arranging liquid crystals with a thin and long molecular structure. A polarization of the molecular arrangement direction is changed according to the size of an electric field when the liquid crystals are arranged in the electric field.
The LCD device essentially has an LCD panel provided with a pair of transparent insulating substrates with a liquid crystal layer interposed therebetween so as to form electric field generating electrodes at their facing surfaces, respectively.
The LCD device artificially controls an arrangement direction of liquid crystal molecules by changing the electric field between the electric field generating electrodes, and displays various images using light transmissivity that is changed by controlling the arrangement direction.
Liquid crystal cells are arranged in a matrix. In order to drive the LCD panel, many peripheral driving circuits surrounding the LCD panel are required.
For example, the LCD panel may comprise a gate driving unit for driving gate lines, a data driving unit for driving data lines, a timing controller for controlling a driving timing of the gate and data driving units, and a power source unit for supplying power source signals required to drive the LCD panel and the driving units.
The gate and data driving units are divided into a plurality of integrated circuits (ICs) to be fabricated in a chip shape.
The integrated driving ICs may respectively be mounted on an IC region, opened on a TCP (Tape Carrier Package) or on a base film of the TCP, by a COF (Chip on Film) method, and may be electrically connected to the LCD panel by a TAB (Tape Automated Bonding) method.
The driving ICs may be directly mounted on the LCD panel by a COG (Chip On Glass) method. The timing controller and the power source unit may be fabricated in chip shapes to be mounted on a main PCB (Printed Circuit Board).
First, the driving ICs connected to the LCD panel by the TCP method are connected to the timing controller and the power source unit on the main PCB via a FPC (Flexible Printed Circuit) and a sub PCB.
In detail, the data driving ICs may receive data control signals and pixel data from the timing controller, which is mounted on the main PCB, and power source signals from the power source unit, all via a data FPC and a data PCB.
The gate driving ICs may receive gate control signals from the timing controller, which is mounted on the main PCB, and power source signals from the power source unit, all via a gate FPC and a gate PCB.
On the other hand, the driving ICs mounted on the LCD panel by the COG method may receive control signals and pixel data from the timing controller, which is mounted on the main PCB, and power source signals from the power source unit, all via the FPC and LOG (Line On Glass) types of signal lines formed on the LCD panel.
In the COG method of the related art, as shown in FIG. 1, FPC wires (lines) corresponding to the number of gamma reference voltages are provided between a man PCB 10 and a data driving IC 14.
Accordingly, a certain gamma reference voltage is applied to a gradation voltage generating unit, which is configured in the data driving IC 14, to create a corresponding gradation voltage. Images can thus be displayed on the LCD panel by the gradation voltage.
However, in the related art, as shown in FIG. 1, a gamma reference voltage generating unit is formed outside the data driving IC 14. A gamma reference voltage, which has been normally applied from the gamma reference voltage generating unit, is applied differently to each data driving IC 14 due to line resistance occurred by the LOG types of signal lines. Accordingly, a different gradation voltage may be created.
In other words, a uniform voltage may not be transferred to a data driving IC, which is located far from the gamma reference voltage generating unit.
As a result, overall resolution of the LCD panel may be unbalanced, namely, an inter-block dim phenomenon may occur.